This invention relates to prosthetic closure devices to replace the valves in human hearts, in particular the mitral and tricuspid valves, having a valve body in the form of a ring, a suture ring for attaching the valve body to the tissue and a valve member positioned in the valve body.
The history of artificial heart valves already covers a period of over twenty-five years and began with the first valve implanted by Hufnagel in 1952. Since then the problems of developing and perfecting artificial heart valves have not been completely solved, which results in the large number of around forty types of valves in use today.
At present spherical and disc valves are the leaders in the field, and also in the last few years replacement valves for special uses made from pig's heart valves have also gained in importance. However, the results obtained with all closure devices of this type are not satisfactory. For example, the average survival rate of patients with an artificial heart valve is still under five years.
The resultant complications can essentially be reduced to four reasons:
flow mechanics reasons, PA1 mechanical reasons, PA1 biological reasons, PA1 material reasons,
or combinations of these four.
Mechanical reasons for a valve defect can be material fatigue, breakage or deformation of a valve either due to mechanical stress or chemical corrosion. Amongst defects of a biological nature, inflammation and rejection of the material which is foreign to the body are frequently encountered. Defects due to flow mechanics, such as destruction of red corpuscles in areas of high localised shear stress and the formation of thromboses in areas of low speed of flow, are further important reasons. Shear stress and distribution of speed with the above-mentioned characteristics are to be found in all valves, since they restrict the blood flow in various ways:
(a) by the valve member itself, which forces the blood to flow through an annular slot between the valve member and the valve body (with spherical or disc valves) or in two separate flow channels with a different form of flow separation (with centrally placed disc valves); PA0 (b) by the valve member mounting support (cages, clamps); and PA0 (c) by the complete valve body, which consists of valve seating and suture ring. PA0 (a) Pressure gradients, which cause increased pumping work, loss of efficiency and insufficient inflation of the heart chamber; PA0 (b) high localised shear stress which causes damage or destruction of the cellular blood components; PA0 (c) back flow on closing of the valve of the order of 5% to 10%, and PA0 (d) formation of thromboses in areas of low speed of flow. PA0 (a) undisturbed flow in the open position, since the dish is wide open and substantially parallel to the inflow direction; PA0 (b) minimal flow resistance and good conduction of the blood to the outflow tract in the closed position, since the dish is then fully embedded in the valve ring and lies parallel to the valve surface; PA0 (c) low shear stress on account of the large opening surface and avoidance of obstructions to flow in the bloodstream; PA0 (d) no "dead water" zones, since there are no flow obstructions; PA0 (e) production and use of the chamber vortex to support the end of the valve; and PA0 (f) completely tight closure. PA0 (a) the direct contact of synthetic material to metal between the valve member and valve ring is avoided (low amount of friction), PA0 (b) the sealing effect is improved with the smooth synthetic material, and PA0 (c) development of noise is reduced.
Contrary to the properties of existing artificial heart valves, natural valves permit a central, undisturbed flow with a smooth opening and closing action and without any back flow. A further great disadvantage of most artificial heart valves is the psychological stress suffered by patients during the noise of opening and closing.
It can therefore be summarised that the currently used types of valves do not satisfactorily comply with functional requirements. The reasons for defects in known valves can be summarised as follows:
The invention is based on the problem of producing a closure device suitable for replacing the valves in human hearts, and especially suitable for the mitral and tricuspid valves, with which the disadvantages previously pointed out can be overcome and in particular a smooth, undisturbed flow both in the open and closed positions can be achieved and "dead water" zones causing thromboses and also high shear stress which is harmful to the blood can be avoided.